For those who don't know Volt-Turn is a strategies used on many teams in the OU tier. It can be used to break both physical and special walls but most importantly giving you momentum, allowing you to switch into a Pokemon advantageous to you and disadvantageous to your opponent.

Arguably the best Volt-Turn pair is Scizor and Rotom-W. They happen to cover each others weaknesses plus get stab on their respected moves.

So any good U-turners/Volt Switchers (or even better pairs) then answer below.
Include needed information like sets and descriptions if need be.
Don't say Rotom-W or Scizor.

Yeah your question was very vague and how you described it suggested you do not know the core strategy to Volt-Turn. Pokemon do not need to cover their weaknesses in Volt-turn though sharing a typing isn't exactly advantageous. Its all about momentum and trying to be at the advantage therefore controlling the match most of the battle. It can be used as Pokemon are switching to keep up the momentum. It just so happens Rotom and Scizor cover each others weaknesses, though that said they rarely ever need to cover each other in that sense.

Volt Switch is a playing style so I edited your question. As it was to vague.

I'm being lazy and not writing out a full answer but magnezone and gliscor make a decent volt-turn core if played right as they cover each others weaknesses (magnezone takes ice and water, glisvor takes fighting, ground and fire) and hit on the physical and special side, but like Redshifts answer mamoswine has a field day with it. Magnezone and any of the kami trio also work if you want more offense and Less bulk

Plenty of pokes, including jellicent, tornadus, and starmie can handle keldeo. Also, you're right this core isn't the best, rotom/scizor is better, but I couldn't think of another decent one for ou at the moment

Off the bat you may notice that Jirachi and Landorus-T do not synergize perfectly. Deal with it. They have decent synergy, Jirachi taking Ice Beams and stuff like a boss, while Landorus can switch in on ground moves all day. Strong Water and Fire type moves do kill this core off somewhat and Mamoswine trolls it insanely hard, but that's what team mates are for and besides that the core works pretty well. Jirachi is quite the multi-tasker, spreading paralyzation, passing Wish support to weakened allies, and trolling so hard by paraflinching, while Landorus makes use of Intimidate to significantly boost his physical bulk, giving him the role of taking most physical moves for the core. Landorus also sets rocks and can still hit very hard despite his low attack investment.

This pair sees Victini take Fire and Ice hits while Rotom-C takes the Water and Ground hits. There's plenty of gaps here - Bug is still x1 for Victini, and Poison is x2 for Rotom-C while Rock is x1 but Leaf Storm will be super effective. There's no Dark or Ghost coverage, but still, I'll assume that these aren't the only Pokemon on your team.

I know that this is far from the perfect pair, but still, Emolga manages to take the Electric hits with Motor Drive, and Lumineon will take the Ice hits.

The Lumineon set doesn't have to be a Rain Dance one, but then again, what else are you going to use it for.

I put an Acrobatics set for Emolga, but a Thunder set is possible as well due to Rain Dance. U-Turn is actually preferable for Acro-Emolga because it's a physical set, and Volt Switch is useless against Ground types like Golurk (which is an ever threat in NU).

Fake Out lead, with Acrobatics and Low Sweep giving coverage. U-Turn to Manectric. Or simply to get out.

These two pokes have wicked speed and wicked attack stats. Together and used properly they can wreck havoc. As Ambipom's only weakness is fighting and that is normally though not always physical, a switch to Manectric can activate Static.

Lightningrod > Static; Manectric's meant to be a sweeper, and it can't be taking a lot of (or any) hits. It's got a base def & sp. def of 60, along with a HP of 70. One switch in to a STAB Fighting move from Cobalion, Mienshao, Heracross, Virizion or Machamp will OHKO it.

Also, Static only has 30% chance of activating. Just like Cursed Body - so annoying. T__T

Cobalion @ Rocky Helmet
Justified
Timid
128 Def, 128 SpA, 252 Spe
Volt-Switch
Focus Blast/Flash Cannon
Stealth Rock
Thunder Wave/Calm Mind
An interesting set that both utilizes his uncommon Volt-Switch, and has the capacity to set up on a weak or non-threatening Pokemon. Now as to Focus Blast and Flash Cannon, if you want power, go Focus Blast, but Flash Cannon also gives great coverage and still obtains STAB. Now the choice between TW and CM is simply, do you want to try to kill the opposition, or do you want to cripple them for later.

I know this set is not the best, but as it has been agreed, Scizor+Rotom-W is the best. They both cover each other pretty well. Cobalion takes Dark types pointed at Azelf like a baws. He also can handle a strong ghost or bug type attack without being KOed. Now as for Azelf, he has leviate which puts Cobalions ground weakness out of concern. The blue balloon can easily soak a psychic type attack but it has trouble taking fire type attakcs due to having no resistance. But overall, they are a great team